Acid leaching of rare earth elements from coal ash obtained from a Mongolian surface mine

Rare earth elements (REEs) are crucial for various renewable and clean technologies, increasing the importance of their recovery from secondary sources. This study determines if REE content and recovery from coal samples, and their ash, could be obtained from a Mongolian coal mine deposit in sufficient quantities for reuse. 9 different coal samples were examined and the highest REE concentrations were found in samples 3, 7, and 4. Upon burning, REEs in the coal ash samples significantly increased in all three samples. Direct acid leaching further improved REE recovery (S3); moreover, when alkali pre-treatment and 1M hydrochloric acid leaching were used, REE recovery was increased even further (sample 7). These findings characterize coal ash at this mining site, and indicate that it could serve as a viable secondary source of REEs, using optimized leaching methods to enhance the effectiveness, for potential industrial applications in Mongolia.